Alot of women aren't able to achieve an orgasm. I think it's a pretty normal thing. You have to feel completely comfortable with yourself and your partner. It wouldn't hurt if you "take some alone time" by yourself either. You can figure out what you like and then be able to tell or show him. I've found that it's easier for me if I'm on top and in control. Luckily I rarely have a problem getting one

Hope it works out for you